Selaginella xanthoneura Valdespino, 2020

Valdespino, Ivan A., 2020, Taxonomic innovations in South American Selaginella (Selaginellaceae, Lycopodiophyta): description of five new species and an additional range extension, PhytoKeys 159, pp. 71-113 : 71

Selaginella xanthoneura Valdespino sp. nov. Figures 5 , 14 , 15 , 16 , 17 , 18

Diagnosis.

Selaginella xanthoneura is distinct from S. hartii Hieron. by lacking (vs. often with) flagelliform stem and branch apices, coriaceous (vs. chartaceous) leaves, lateral leaves ovate to broadly ovate (vs. ovate-oblong) with rounded (vs. truncate) bases and shortly ciliate (vs. denticulate) acroscopic margins, and acroscopic halves near proximal ⅓ of the lamina about the same width of (vs. twice as wide as) basiscopic halves, and median leaf outer margins distinctly widely hyaline (vs. green) with acuminate to short-aristate (vs. long-aristate) apices, each acumen or arista 0.1-0.3 (vs. 1.0) mm long.

Type.

Colombia. Magdalena [La Guajira]: Sierra de Perijá, 10 km ENE of Manaure, 46 km E of Valledupar, 3 km from the Venezuelan border, 2300 m, 4 Feb 1945 (fe), M. Grant 10811 (holotype: COL!; isotypes: CR!, GH!, NY!, US-2 sheets!).

Description.

Plants terrestrial. Stems erect, stramineous, 28-60 cm tall, (0.5)1.0-2.5 mm diam. on main stem before first branches, non-articulate, not flagelliform, stoloniferous, 2 or 3-branched, the terminal portion of the stem similar in shape to lateral branches (i.e., conform). Rhizophores axillary, ventral, dorsal, and seemingly lateral, borne on lower-most part of the stems and throughout stolons, stout, 0.2-0.5 mm diam. Leaves seemingly monomorphic and strongly appressed to the stems up to shortly before (ca. 3 cm below) first branch, then heteromorphic throughout, coriaceous, upper surfaces shiny greenish yellow (i.e., citrine) when dry, smooth to slightly striate, lower surfaces shiny to silvery greenish-yellow, striate submedially and smooth towards margins, those on main stems before fully heteromorphic ovate-deltate or deltate, the bases prominently raised and truncate with both edges rounded or slightly subcordate and entire or denticulate, the margins narrowly to broadly hyaline, greenish-hyaline or greenish, inner margins short-ciliate along proximal ¼, otherwise dentate to denticulate distally, outer margins dentate to denticulate distally, apices acute, tipped by 1-4 teeth or entire. Lateral leaves on main stem after leaves fully heteromorphic, imbricate and ascending up to proximal ½ of the stems, otherwise distant and spreading along distal ½ of the stems, ovate to broadly ovate ascending, 4.0-6.0 × (1.5)2.0-3.5 mm; bases rounded to subcordate with a truncate and prominent central portion, glabrous, acroscopic bases strongly overlapping stems, rounded, basiscopic bases free from stems, rounded; margins on upper surfaces narrowly bordered by greenish, rectangular, and laevigate cells, acroscopic margins on lower surfaces bordered continuously by a hyaline band comprised of idioblasts, the band 2-7 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, basiscopic margins on proximal ⅓ bordered by elongate, greenish, rectangular, and laevigate cells and submarginally bordered by a hyaline band comprised of idioblasts, the band 1-5 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, on distal ⅔ bordered by a hyaline band comprised of idioblasts, the band 3-10 cells wide, the idioblasts similar to those of the acroscopic margins and submarginal proximal ⅓ of basiscopic margins and often specially toward distal ⅓ intermixed with cells similar to those of basiscopic proximal ⅓; apices acute to shortly attenuate, tipped by 1-3 teeth; upper surfaces comprising irregularly shaped, somewhat rectangular to quadrangular, sinuate-walled cells, with some sparingly distributed short, quadrangular to round, papillate idioblasts, each idioblast cell lumen with 5-8 papillae, without stomata, lower surfaces comprised of elongate, sinuate-walled cells and of elongate, straight-walled, papillate idioblasts, each idioblast cell lumen with 8-45 papillae in 1-3 rows, stomata on 1-6 rows along midribs. Median leaves on main stem after leaves fully heteromorphic, distant, ascending, broadly ovate, ovate-elliptic or ovate-lanceolate, 2.0-4.0 × 1.3-2.0 mm; bases glabrous, subcordate with a prominent, round outer lobe, without auricles; inner margins on upper surfaces bordered continuously by a narrowly hyaline band of idioblasts along distal ¾, the band 1-4 cells wide, the idioblasts similar to those in the hyaline marginal bands of lateral leaves acroscopic margins on lower surfaces of lateral leaves, the outer margins on upper surfaces obscurely greenish and comprising elongate, straight-walled, glabrous cells along proximal ⅓- ½, on proximal ⅓- ½ submargins and distal ½ -⅔ margins bordered continuously by a hyaline band of idioblasts, the idioblasts similar to those in the hyaline marginal bands of lateral leaves acroscopic margins on lower surfaces but the band 2-7 cells wide and with one or two rows of papillae on cell lumen, entire along proximal ⅓ and shortly ciliate along distal ⅔; apices acuminate to short-aristate, each acumen or arista 0.1-0.3 long, tipped by 1-3 teeth; upper surfaces comprising quadrangular, rectangular to roundish, sinuate-walled cells and many, evenly distributed papillate idioblasts, each idioblasts with 5-12 papillae, stomata in 1-4 rows on distal ⅔- ¾ along the midribs and marginal to submarginal along proximal ⅓ of outer margins, lower surfaces comprising elongate, straight-walled cells, without idioblasts, except for idioblasts present along proximal submarginal portion of outer margins where the idioblast are similar to those on distal ½ -⅔ of outer margin on upper surfaces, without stomata. Axillary leaves on main stem after leaves fully heteromorphic similar in shape to lateral leaves or narrowly ovate, 3.5-4.4 × 1.5-2.4 mm; bases similar to those of lateral leaves; margins on upper and lower surfaces as those in margins of lateral leaves; apices as those of lateral leaves; both surfaces similar to those of lateral leaves. Strobili terminal on branch tips, quadrangular, 0.4-1.0 cm long. Sporophylls monomorphic, without a laminar flap, each with a slightly developed keel along midribs, the keel glabrous or with few, short, tooth-like projections distally, ovate-lanceolate, 1.4-2.0 × 0.5-1.0 mm; bases rounded; margins narrowly hyaline, 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and glabrous, parallel to margins, shortly ciliate along proximal ½, denticulate on distal ½ or denticulate throughout; apices long-attenuate to long-acuminate, the acumen 0.1 or 0.2 mm long, tipped by 1 tooth; dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls where the surfaces are greenish hyaline with elongate and slightly sinuate-walled cells, lower surfaces silvery green and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces, silvery green to hyaline, comprised of elongate, papillate, sinuate-walled cells. Megasporangia few on two proximal ventral rows; megaspores yellow, 100-120 µm diam., proximal faces rugulate-reticulate with a well-developed equatorial flange, the microstructure perforate and echinate, distal faces reticulate, the reticula closed, the microstructure granulate and perforate. Microsporangia on two dorsal rows and along most of two ventral rows; microspores light orange, 25-30 µm diam., proximal faces rugulate, the microstructure echinate and perforate, distal faces capitate, with each caput microechinate, the rest of the microstructure echinate and perforate.

Habitat and distribution.

Selaginella xanthoneura grows in tropical montane rainforests at 1800-2300 m. It is known from Serranía del Perijá, an extension of the eastern Andean branch (Western Cordillera) in the state of Magdalena, and in the isolated mountain range of Sierra Nevada de Santa Marta, states of César and Magdalena, both in northern Colombia, and is expected to also occur in the neighboring state of Zulia, Venezuela. It has been collected in fertile condition from February to June.

Etymology.

The specific epithet derives from the Gr. " xanthos," yellow, and " neuron," nerve, referring to the conspicuous yellow, leaf midribs on upper surfaces.

Conservation status.

Selaginella xanthoneura is known from only six collections made in two adjacent Colombian Departments, growing at high elevations, probably in and around protected areas, which however are imperiled by human encroachments and natural adversities such as landslides. It might eventually prove to be present in adjacent areas in Venezuela, but there is no current documentation to support this. It might well be that this species is relatively well protected, but the limited number of documented occurrences and distribution, as well as possible threats enumerated above indicate that it should be considered Vulnerable (VU) based on IUCN (2012).

Additional specimens examined (paratypes).

Colombia. César: Santa Marta, between Playoncito and Cuchilla Monogaca N, Pueblo Bello, 1900 m, 4 Feb 1967, Mägdefrau 1247 (UC); Sierra Nevada de Santa Marta, Playoncito an Clisndivana? [illegible], 1800 m, Jun 1928, Schultze 1518 (B, BM, PMA); Mpio. Manaure, Serranía del Perijá El Cinco, Finca Vistahermosa, SE de la carretera, 10°26'N, 72°57'W, 2200 m, 13 Nov 1993, Rangel et al. 11420 (COL-image), 2235 m, 14 Nov 1993, Pardo et al. 304 (COL-image). Magdalena: Sierra Neva de Santa Marta, entre San Pedro y cabeceras del Río Sevilla, slopes of La Cebolleta and Yerba Buena, ca. 2300 m and lower, 1 Feb 1959, Barclay & Juajibioy 6808 (MO-2 sheets).

Discussion.

Selaginella xanthoneura is characterized by its fern-like habit, erect stems, each 28-60 cm tall, leaves on main stems shortly (ca. 3 cm) before first branches seemingly monomorphic and strongly appressed, the leaves after becoming fully heteromorphic with shiny, greenish yellow (i.e., citrine) upper surfaces when dry and yellowish to stramineous midribs. It is further distinguished by its median leaf bases subcordate with a prominent, round outer lobe, outer margins along proximal, submarginal ⅓- ½ and distal, marginal ½ -⅔ continuously bordered by a hyaline band of idioblasts, and acuminate to short-aristate apices, the upper surfaces of median leaves and the lower surfaces of lateral leaves with papillate idioblasts, and relatively short strobili, each 0.4-1.0 cm long, and with few megasporangia restricted to proximal portion of two rows of strobili ventral sporophylls.

Interestingly, one examined duplicate specimens of S. xanthoneura (Schultze 1518, B) has vegetative growth from strobili tips. This is a feature that has been amply documented in other morphologically related members of the " Selaginella flabellata group," as well as on unrelated taxa from different regions of the world (Hieronymus 1901; Williams 1931; Jermy 1990; Valdespino 1993a, 1993b; Valdespino 1995; Zhang et al. 2014; Valdespino et al. 2015) and for which specific patterns were described ( Valdespino et al. 2015). This same collection (Schultze 1518) at B and BM was originally determined by Alston as S. hartii , which certainly is somewhat similar to S. xanthoneura because of their overall fern-like habit with erect stems and leaves fully dimorphic shortly before first stem branches. Selaginella xanthoneura is easily set aside from the latter species by characters listed in the diagnosis. In addition, S. xanthoneura , at present, is only known to occur in Colombia, whereas S. hartii is only known from Trinidad and Tobago and the Peninsula of Paria in Sucre state, Venezuela. Furthermore, S. xanthoneura has a more robust plant habit with stems 2 or 3- (vs. 1 or 2 or occasionally 3-) branched.

Selaginella xanthoneura , as well as other members of the " Selaginella flabellata group," such as S. cheiromorpha Alston, S. hartwegiana Spring, and S. mosorongensis Hieron. all have similar median and lateral leaf shapes. Nevertheless, S. xanthoneura differs from all those species by its median leaf outer bases lacking a distinct auricle and having conspicuously yellow to yellowish lateral and median leaf midribs. Selaginella xanthoneura is further set aside from S. mosorongensis by its entire (vs ciliate) median leaf outer bases.

Figures

Figure 5. Distribution of Selaginella gioiae □, S. surucucusensis ▲, S. xanthoneura ●.

Figure 14. Selaginella xanthoneura Valdespino. A Habit, upper surface of stem B branch section, upper surface, note terminal strobilus C branch section, lower surface D branch section showing median leaves, upper surfaces E, F branch section showing axillary leaf (E) and lateral leaf (F), lower surfaces. A-F line drawing made from the holotype and isotypes as follow: A, C-D. E, F (holotype) and B (isotypes at GH & NY). Illustration by Haruto Fukuda.

Figure 15. Selaginella xanthoneura Valdespino. A Lateral leaf from stem, upper surface. B proximal half of lateral leaf, upper surface (same leaf shown in A) C distal half of lateral leaf, upper surface (same leaf shown in A) D lateral leaf, lower surface E proximal half of lateral leaf, lower surface (same leaf shown in D) F distal half of lateral leaf, lower surface (same leaf shown in D); note, submarginal, elongate and papillate idioblasts (F 1) G median leaf from stem branch, upper surface H proximal half of lateral leaf, upper surface (same leaf shown in G); note submarginal band of idioblasts (a) and stomata along midrib (b) I distal half of median leaf, upper surface (same leaf shown in G); note, short elongate and papillate idioblasts (a). A-I taken from the holotype.

Figure 16. Selaginella xanthoneura Valdespino. A median leaf from stem, lower surface B proximal, inner half section of median leaf, lower surface (same leaf shown in A); note elongate and papillate idioblasts (a) C detail of papillae on idioblasts present on inner half section of median leaf, lower surface (same leaf shown in A) D axillary leaf from stem branch, upper surface E proximal half of axillary leaf, upper surface (same leaf shown in D) F distal half of axillary leaf, upper surface (same leaf shown in D). A-F taken from the holotype.

Figure 17. Selaginella xanthoneura Valdespino. A Megaspore, proximal face B detail of megaspore, proximal face C megaspore, distal face D detail of megaspore, distal face. A-D taken from the holotype.

Figure 18. Selaginella xanthoneura Valdespino. A Microspore, proximal face B detail of microspore, proximal face C microspore, distal face D detail of microspore, distal face E microspore, distal face, equatorial view F detail of capitate projections with echinate microstructure surfaces. A-F taken from the holotype.